1. Field of the Invention
The invention relates to a lubricant gun, more particularly to a battery-operated lubricant gun.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional battery-operated grease gun disclosed in U.S. Pat. No. 6,135,327 includes a housing 1, a lubricant reservoir 2, an electric motor 3, a power transmission 4, a yoke 5, and a plunger 6. The housing 1 has a motor and transmission compartment 101, a handle 102, a discharge spout 103 contained in the front portion of the motor and transmission compartment 101, and a cylindrical pump chamber 104 mounted along an axial direction and fluidly communicated with the discharge spout 103. The lubricant reservoir 2 is connected to the motor and transmission compartment 101. Lubricant can be supplied from the lubricant reservoir 2 into the cylindrical pump chamber 104. The electric motor 3 is mounted within the rear portion of the motor and transmission compartment 101. The power transmission 4 is driven by the electric motor 3, and includes a planetary gearing set 401, a final driver 402, and a drive pin 403 connected eccentrically to and disposed below the final driver 402. The yoke 5 has a cam slot 501 for sliding the drive pin 403 therethrough freely from end to end. The plunger 6 is driven by the yoke 5 to reciprocate in the pump chamber 104. The planetary gearing set 401 has a three-staged configuration, and is mounted on the final driver 402. The final driver 402 is rotatably engaged to the motor and transmission compartment 101 via a bearing 404. When the electric motor 3 is activated, the planetary gearing set 401 is rotated and transforms the output of the electric motor 3, reducing its speed as it is transmitted to the final driver 402 for causing rotation of the final driver 402. The rotation of the final driver 402 is transmitted to the yoke 5 by the drive pin 403 so as to cause the yoke 5 to slide in reciprocating movement. The sliding reciprocating movement of the yoke 5 is transmitted to the plunger 6, causing it to reciprocate through the pump chamber 104. The reciprocation of the plunger 6 enables the lubricant to be pushed through the pump chamber 104 and to be discharged through the discharge spout 103. Although the lubricant can be discharged via the reciprocating movement of the plunger 6 caused by the reciprocating movement of the yoke 5, the aforesaid grease gun has the following shortcomings:
1. Since the yoke 5 is a relatively massive block, the reciprocating movement of the yoke 5 may impose a significant impact on the housing 1, which leads to the shaking of the housing 1. Therefore, it is not easy to hold the grease gun stably.
2. Referring to FIG. 2, the yoke 5 is positioned between two opposite side walls 1012 of the motor and transmission compartment 101, and slides across a pair of sliding rails 1011. However, as mentioned above, since the yoke 5 is a relatively massive block, the reciprocating movement of the yoke 5 may produce a significant friction between the yoke 5 and the side walls 1012 as well as the sliding rails 1011, which results in an increase in the power load of the electric motor 3.
Referring to FIG. 3, in another conventional battery-operated grease gun disclosed in U.S. Pat. No. 5,105,912, a driving member 7 includes a drive wheel 701 driven by an electric motor 704, a piston 702 slidably mounted in a chamber 801 of a housing 8, and a connecting arm 703 pivotally interconnecting the drive wheel 701 and the piston 702. When the drive wheel 701 is driven, the rotation of the drive wheel 701 will cause reciprocating movement of the piston 702 in the chamber 801 via the connecting arm 703 so that the lubricant can be discharged out of the housing 8. The connecting arm 703 is relatively light in weight. Furthermore, there is no friction between the connecting arm 703 and the housing 8. Therefore, the aforesaid shortcomings attributed to the yoke 5 in the grease gun disclosed in U.S. Pat. No. 6,135,327 will not occur in the grease gun disclosed in U.S. Pat. No. 5,105,912. However, referring to FIG. 4, when the drive wheel 701 is intended to push the portion of the piston 702 exposed outside the chamber 801 back into the chamber 801, a transverse torque (L×Fx) is imposed on the piston 702, which will lead to deformation or breakage of the piston 702. The friction between the chamber 801 and piston 702 may also occur due to the tilting of the piston 702.